lib/rhashtable.c

   1 /*
   2  * Resizable, Scalable, Concurrent Hash Table
   3  *
   4  * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
   5  * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>
   6  * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
   7  *
   8  * Code partially derived from nft_hash
   9  * Rewritten with rehash code from br_multicast plus single list
  10  * pointer as suggested by Josh Triplett
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License version 2 as
  14  * published by the Free Software Foundation.
  15  */
  16
  17 #include <linux/atomic.h>
  18 #include <linux/kernel.h>
  19 #include <linux/init.h>
  20 #include <linux/log2.h>
  21 #include <linux/sched.h>
  22 #include <linux/slab.h>
  23 #include <linux/vmalloc.h>
  24 #include <linux/mm.h>
  25 #include <linux/jhash.h>
  26 #include <linux/random.h>
  27 #include <linux/rhashtable.h>
  28 #include <linux/err.h>
  29 #include <linux/export.h>
  30
  31 #define HASH_DEFAULT_SIZE       64UL
  32 #define HASH_MIN_SIZE           4U
  33 #define BUCKET_LOCKS_PER_CPU   128UL
  34
  35 static u32 head_hashfn(struct rhashtable *ht,
  36                        const struct bucket_table *tbl,
  37                        const struct rhash_head *he)
  38 {
  39         return rht_head_hashfn(ht, tbl, he, ht->p);
  40 }
  41
  42 #ifdef CONFIG_PROVE_LOCKING
  43 #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
  44
  45 int lockdep_rht_mutex_is_held(struct rhashtable *ht)
  46 {
  47         return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
  48 }
  49 EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
  50
  51 int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
  52 {
  53         spinlock_t *lock = rht_bucket_lock(tbl, hash);
  54
  55         return (debug_locks) ? lockdep_is_held(lock) : 1;
  56 }
  57 EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
  58 #else
  59 #define ASSERT_RHT_MUTEX(HT)
  60 #endif
  61
  62
  63 static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl,
  64                               gfp_t gfp)
  65 {
  66         unsigned int i, size;
  67 #if defined(CONFIG_PROVE_LOCKING)
  68         unsigned int nr_pcpus = 2;
  69 #else
  70         unsigned int nr_pcpus = num_possible_cpus();
  71 #endif
  72
  73         nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL);
  74         size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul);
  75
  76         /* Never allocate more than 0.5 locks per bucket */
  77         size = min_t(unsigned int, size, tbl->size >> 1);
  78
  79         if (sizeof(spinlock_t) != 0) {
  80 #ifdef CONFIG_NUMA
  81                 if (size * sizeof(spinlock_t) > PAGE_SIZE &&
  82                     gfp == GFP_KERNEL)
  83                         tbl->locks = vmalloc(size * sizeof(spinlock_t));
  84                 else
  85 #endif
  86                 tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
  87                                            gfp);
  88                 if (!tbl->locks)
  89                         return -ENOMEM;
  90                 for (i = 0; i < size; i++)
  91                         spin_lock_init(&tbl->locks[i]);
  92         }
  93         tbl->locks_mask = size - 1;
  94
  95         return 0;
  96 }
  97
  98 static void bucket_table_free(const struct bucket_table *tbl)
  99 {
 100         if (tbl)
 101                 kvfree(tbl->locks);
 102
 103         kvfree(tbl);
 104 }
 105
 106 static void bucket_table_free_rcu(struct rcu_head *head)
 107 {
 108         bucket_table_free(container_of(head, struct bucket_table, rcu));
 109 }
 110
 111 static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 112                                                size_t nbuckets,
 113                                                gfp_t gfp)
 114 {
 115         struct bucket_table *tbl = NULL;
 116         size_t size;
 117         int i;
 118
 119         size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
 120         if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER) ||
 121             gfp != GFP_KERNEL)
 122                 tbl = kzalloc(size, gfp | __GFP_NOWARN | __GFP_NORETRY);
 123         if (tbl == NULL && gfp == GFP_KERNEL)
 124                 tbl = vzalloc(size);
 125         if (tbl == NULL)
 126                 return NULL;
 127
 128         tbl->size = nbuckets;
 129
 130         if (alloc_bucket_locks(ht, tbl, gfp) < 0) {
 131                 bucket_table_free(tbl);
 132                 return NULL;
 133         }
 134
 135         INIT_LIST_HEAD(&tbl->walkers);
 136
 137         get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
 138
 139         for (i = 0; i < nbuckets; i++)
 140                 INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);
 141
 142         return tbl;
 143 }
 144
 145 static struct bucket_table *rhashtable_last_table(struct rhashtable *ht,
 146                                                   struct bucket_table *tbl)
 147 {
 148         struct bucket_table *new_tbl;
 149
 150         do {
 151                 new_tbl = tbl;
 152                 tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 153         } while (tbl);
 154
 155         return new_tbl;
 156 }
 157
 158 static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)
 159 {
 160         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 161         struct bucket_table *new_tbl = rhashtable_last_table(ht,
 162                 rht_dereference_rcu(old_tbl->future_tbl, ht));
 163         struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];
 164         int err = -ENOENT;
 165         struct rhash_head *head, *next, *entry;
 166         spinlock_t *new_bucket_lock;
 167         unsigned int new_hash;
 168
 169         rht_for_each(entry, old_tbl, old_hash) {
 170                 err = 0;
 171                 next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
 172
 173                 if (rht_is_a_nulls(next))
 174                         break;
 175
 176                 pprev = &entry->next;
 177         }
 178
 179         if (err)
 180                 goto out;
 181
 182         new_hash = head_hashfn(ht, new_tbl, entry);
 183
 184         new_bucket_lock = rht_bucket_lock(new_tbl, new_hash);
 185
 186         spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING);
 187         head = rht_dereference_bucket(new_tbl->buckets[new_hash],
 188                                       new_tbl, new_hash);
 189
 190         RCU_INIT_POINTER(entry->next, head);
 191
 192         rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
 193         spin_unlock(new_bucket_lock);
 194
 195         rcu_assign_pointer(*pprev, next);
 196
 197 out:
 198         return err;
 199 }
 200
 201 static void rhashtable_rehash_chain(struct rhashtable *ht,
 202                                     unsigned int old_hash)
 203 {
 204         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 205         spinlock_t *old_bucket_lock;
 206
 207         old_bucket_lock = rht_bucket_lock(old_tbl, old_hash);
 208
 209         spin_lock_bh(old_bucket_lock);
 210         while (!rhashtable_rehash_one(ht, old_hash))
 211                 ;
 212         old_tbl->rehash++;
 213         spin_unlock_bh(old_bucket_lock);
 214 }
 215
 216 static int rhashtable_rehash_attach(struct rhashtable *ht,
 217                                     struct bucket_table *old_tbl,
 218                                     struct bucket_table *new_tbl)
 219 {
 220         /* Protect future_tbl using the first bucket lock. */
 221         spin_lock_bh(old_tbl->locks);
 222
 223         /* Did somebody beat us to it? */
 224         if (rcu_access_pointer(old_tbl->future_tbl)) {
 225                 spin_unlock_bh(old_tbl->locks);
 226                 return -EEXIST;
 227         }
 228
 229         /* Make insertions go into the new, empty table right away. Deletions
 230          * and lookups will be attempted in both tables until we synchronize.
 231          */
 232         rcu_assign_pointer(old_tbl->future_tbl, new_tbl);
 233
 234         /* Ensure the new table is visible to readers. */
 235         smp_wmb();
 236
 237         spin_unlock_bh(old_tbl->locks);
 238
 239         return 0;
 240 }
 241
 242 static int rhashtable_rehash_table(struct rhashtable *ht)
 243 {
 244         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 245         struct bucket_table *new_tbl;
 246         struct rhashtable_walker *walker;
 247         unsigned int old_hash;
 248
 249         new_tbl = rht_dereference(old_tbl->future_tbl, ht);
 250         if (!new_tbl)
 251                 return 0;
 252
 253         for (old_hash = 0; old_hash < old_tbl->size; old_hash++)
 254                 rhashtable_rehash_chain(ht, old_hash);
 255
 256         /* Publish the new table pointer. */
 257         rcu_assign_pointer(ht->tbl, new_tbl);
 258
 259         spin_lock(&ht->lock);
 260         list_for_each_entry(walker, &old_tbl->walkers, list)
 261                 walker->tbl = NULL;
 262         spin_unlock(&ht->lock);
 263
 264         /* Wait for readers. All new readers will see the new
 265          * table, and thus no references to the old table will
 266          * remain.
 267          */
 268         call_rcu(&old_tbl->rcu, bucket_table_free_rcu);
 269
 270         return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0;
 271 }
 272
 273 /**
 274  * rhashtable_expand - Expand hash table while allowing concurrent lookups
 275  * @ht:         the hash table to expand
 276  *
 277  * A secondary bucket array is allocated and the hash entries are migrated.
 278  *
 279  * This function may only be called in a context where it is safe to call
 280  * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
 281  *
 282  * The caller must ensure that no concurrent resizing occurs by holding
 283  * ht->mutex.
 284  *
 285  * It is valid to have concurrent insertions and deletions protected by per
 286  * bucket locks or concurrent RCU protected lookups and traversals.
 287  */
 288 static int rhashtable_expand(struct rhashtable *ht)
 289 {
 290         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
 291         int err;
 292
 293         ASSERT_RHT_MUTEX(ht);
 294
 295         old_tbl = rhashtable_last_table(ht, old_tbl);
 296
 297         new_tbl = bucket_table_alloc(ht, old_tbl->size * 2, GFP_KERNEL);
 298         if (new_tbl == NULL)
 299                 return -ENOMEM;
 300
 301         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
 302         if (err)
 303                 bucket_table_free(new_tbl);
 304
 305         return err;
 306 }
 307
 308 /**
 309  * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
 310  * @ht:         the hash table to shrink
 311  *
 312  * This function shrinks the hash table to fit, i.e., the smallest
 313  * size would not cause it to expand right away automatically.
 314  *
 315  * The caller must ensure that no concurrent resizing occurs by holding
 316  * ht->mutex.
 317  *
 318  * The caller must ensure that no concurrent table mutations take place.
 319  * It is however valid to have concurrent lookups if they are RCU protected.
 320  *
 321  * It is valid to have concurrent insertions and deletions protected by per
 322  * bucket locks or concurrent RCU protected lookups and traversals.
 323  */
 324 static int rhashtable_shrink(struct rhashtable *ht)
 325 {
 326         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
 327         unsigned int size;
 328         int err;
 329
 330         ASSERT_RHT_MUTEX(ht);
 331
 332         size = roundup_pow_of_two(atomic_read(&ht->nelems) * 3 / 2);
 333         if (size < ht->p.min_size)
 334                 size = ht->p.min_size;
 335
 336         if (old_tbl->size <= size)
 337                 return 0;
 338
 339         if (rht_dereference(old_tbl->future_tbl, ht))
 340                 return -EEXIST;
 341
 342         new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
 343         if (new_tbl == NULL)
 344                 return -ENOMEM;
 345
 346         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
 347         if (err)
 348                 bucket_table_free(new_tbl);
 349
 350         return err;
 351 }
 352
 353 static void rht_deferred_worker(struct work_struct *work)
 354 {
 355         struct rhashtable *ht;
 356         struct bucket_table *tbl;
 357         int err = 0;
 358
 359         ht = container_of(work, struct rhashtable, run_work);
 360         mutex_lock(&ht->mutex);
 361
 362         tbl = rht_dereference(ht->tbl, ht);
 363         tbl = rhashtable_last_table(ht, tbl);
 364
 365         if (rht_grow_above_75(ht, tbl))
 366                 rhashtable_expand(ht);
 367         else if (ht->p.automatic_shrinking && rht_shrink_below_30(ht, tbl))
 368                 rhashtable_shrink(ht);
 369
 370         err = rhashtable_rehash_table(ht);
 371
 372         mutex_unlock(&ht->mutex);
 373
 374         if (err)
 375                 schedule_work(&ht->run_work);
 376 }
 377
 378 static bool rhashtable_check_elasticity(struct rhashtable *ht,
 379                                         struct bucket_table *tbl,
 380                                         unsigned int hash)
 381 {
 382         unsigned int elasticity = ht->elasticity;
 383         struct rhash_head *head;
 384
 385         rht_for_each(head, tbl, hash)
 386                 if (!--elasticity)
 387                         return true;
 388
 389         return false;
 390 }
 391
 392 int rhashtable_insert_rehash(struct rhashtable *ht)
 393 {
 394         struct bucket_table *old_tbl;
 395         struct bucket_table *new_tbl;
 396         struct bucket_table *tbl;
 397         unsigned int size;
 398         int err;
 399
 400         old_tbl = rht_dereference_rcu(ht->tbl, ht);
 401         tbl = rhashtable_last_table(ht, old_tbl);
 402
 403         size = tbl->size;
 404
 405         if (rht_grow_above_75(ht, tbl))
 406                 size *= 2;
 407         /* Do not schedule more than one rehash */
 408         else if (old_tbl != tbl)
 409                 return -EBUSY;
 410
 411         new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC);
 412         if (new_tbl == NULL) {
 413                 /* Schedule async resize/rehash to try allocation
 414                  * non-atomic context.
 415                  */
 416                 schedule_work(&ht->run_work);
 417                 return -ENOMEM;
 418         }
 419
 420         err = rhashtable_rehash_attach(ht, tbl, new_tbl);
 421         if (err) {
 422                 bucket_table_free(new_tbl);
 423                 if (err == -EEXIST)
 424                         err = 0;
 425         } else
 426                 schedule_work(&ht->run_work);
 427
 428         return err;
 429 }
 430 EXPORT_SYMBOL_GPL(rhashtable_insert_rehash);
 431
 432 int rhashtable_insert_slow(struct rhashtable *ht, const void *key,
 433                            struct rhash_head *obj,
 434                            struct bucket_table *tbl)
 435 {
 436         struct rhash_head *head;
 437         unsigned int hash;
 438         int err;
 439
 440         tbl = rhashtable_last_table(ht, tbl);
 441         hash = head_hashfn(ht, tbl, obj);
 442         spin_lock_nested(rht_bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);
 443
 444         err = -EEXIST;
 445         if (key && rhashtable_lookup_fast(ht, key, ht->p))
 446                 goto exit;
 447
 448         err = -E2BIG;
 449         if (unlikely(rht_grow_above_max(ht, tbl)))
 450                 goto exit;
 451
 452         err = -EAGAIN;
 453         if (rhashtable_check_elasticity(ht, tbl, hash) ||
 454             rht_grow_above_100(ht, tbl))
 455                 goto exit;
 456
 457         err = 0;
 458
 459         head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
 460
 461         RCU_INIT_POINTER(obj->next, head);
 462
 463         rcu_assign_pointer(tbl->buckets[hash], obj);
 464
 465         atomic_inc(&ht->nelems);
 466
 467 exit:
 468         spin_unlock(rht_bucket_lock(tbl, hash));
 469
 470         return err;
 471 }
 472 EXPORT_SYMBOL_GPL(rhashtable_insert_slow);
 473
 474 /**
 475  * rhashtable_walk_init - Initialise an iterator
 476  * @ht:         Table to walk over
 477  * @iter:       Hash table Iterator
 478  *
 479  * This function prepares a hash table walk.
 480  *
 481  * Note that if you restart a walk after rhashtable_walk_stop you
 482  * may see the same object twice.  Also, you may miss objects if
 483  * there are removals in between rhashtable_walk_stop and the next
 484  * call to rhashtable_walk_start.
 485  *
 486  * For a completely stable walk you should construct your own data
 487  * structure outside the hash table.
 488  *
 489  * This function may sleep so you must not call it from interrupt
 490  * context or with spin locks held.
 491  *
 492  * You must call rhashtable_walk_exit if this function returns
 493  * successfully.
 494  */
 495 int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter)
 496 {
 497         iter->ht = ht;
 498         iter->p = NULL;
 499         iter->slot = 0;
 500         iter->skip = 0;
 501
 502         iter->walker = kmalloc(sizeof(*iter->walker), GFP_KERNEL);
 503         if (!iter->walker)
 504                 return -ENOMEM;
 505
 506         mutex_lock(&ht->mutex);
 507         iter->walker->tbl = rht_dereference(ht->tbl, ht);
 508         list_add(&iter->walker->list, &iter->walker->tbl->walkers);
 509         mutex_unlock(&ht->mutex);
 510
 511         return 0;
 512 }
 513 EXPORT_SYMBOL_GPL(rhashtable_walk_init);
 514
 515 /**
 516  * rhashtable_walk_exit - Free an iterator
 517  * @iter:       Hash table Iterator
 518  *
 519  * This function frees resources allocated by rhashtable_walk_init.
 520  */
 521 void rhashtable_walk_exit(struct rhashtable_iter *iter)
 522 {
 523         mutex_lock(&iter->ht->mutex);
 524         if (iter->walker->tbl)
 525                 list_del(&iter->walker->list);
 526         mutex_unlock(&iter->ht->mutex);
 527         kfree(iter->walker);
 528 }
 529 EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
 530
 531 /**
 532  * rhashtable_walk_start - Start a hash table walk
 533  * @iter:       Hash table iterator
 534  *
 535  * Start a hash table walk.  Note that we take the RCU lock in all
 536  * cases including when we return an error.  So you must always call
 537  * rhashtable_walk_stop to clean up.
 538  *
 539  * Returns zero if successful.
 540  *
 541  * Returns -EAGAIN if resize event occured.  Note that the iterator
 542  * will rewind back to the beginning and you may use it immediately
 543  * by calling rhashtable_walk_next.
 544  */
 545 int rhashtable_walk_start(struct rhashtable_iter *iter)
 546         __acquires(RCU)
 547 {
 548         struct rhashtable *ht = iter->ht;
 549
 550         mutex_lock(&ht->mutex);
 551
 552         if (iter->walker->tbl)
 553                 list_del(&iter->walker->list);
 554
 555         rcu_read_lock();
 556
 557         mutex_unlock(&ht->mutex);
 558
 559         if (!iter->walker->tbl) {
 560                 iter->walker->tbl = rht_dereference_rcu(ht->tbl, ht);
 561                 return -EAGAIN;
 562         }
 563
 564         return 0;
 565 }
 566 EXPORT_SYMBOL_GPL(rhashtable_walk_start);
 567
 568 /**
 569  * rhashtable_walk_next - Return the next object and advance the iterator
 570  * @iter:       Hash table iterator
 571  *
 572  * Note that you must call rhashtable_walk_stop when you are finished
 573  * with the walk.
 574  *
 575  * Returns the next object or NULL when the end of the table is reached.
 576  *
 577  * Returns -EAGAIN if resize event occured.  Note that the iterator
 578  * will rewind back to the beginning and you may continue to use it.
 579  */
 580 void *rhashtable_walk_next(struct rhashtable_iter *iter)
 581 {
 582         struct bucket_table *tbl = iter->walker->tbl;
 583         struct rhashtable *ht = iter->ht;
 584         struct rhash_head *p = iter->p;
 585
 586         if (p) {
 587                 p = rht_dereference_bucket_rcu(p->next, tbl, iter->slot);
 588                 goto next;
 589         }
 590
 591         for (; iter->slot < tbl->size; iter->slot++) {
 592                 int skip = iter->skip;
 593
 594                 rht_for_each_rcu(p, tbl, iter->slot) {
 595                         if (!skip)
 596                                 break;
 597                         skip--;
 598                 }
 599
 600 next:
 601                 if (!rht_is_a_nulls(p)) {
 602                         iter->skip++;
 603                         iter->p = p;
 604                         return rht_obj(ht, p);
 605                 }
 606
 607                 iter->skip = 0;
 608         }
 609
 610         iter->p = NULL;
 611
 612         /* Ensure we see any new tables. */
 613         smp_rmb();
 614
 615         iter->walker->tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 616         if (iter->walker->tbl) {
 617                 iter->slot = 0;
 618                 iter->skip = 0;
 619                 return ERR_PTR(-EAGAIN);
 620         }
 621
 622         return NULL;
 623 }
 624 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
 625
 626 /**
 627  * rhashtable_walk_stop - Finish a hash table walk
 628  * @iter:       Hash table iterator
 629  *
 630  * Finish a hash table walk.
 631  */
 632 void rhashtable_walk_stop(struct rhashtable_iter *iter)
 633         __releases(RCU)
 634 {
 635         struct rhashtable *ht;
 636         struct bucket_table *tbl = iter->walker->tbl;
 637
 638         if (!tbl)
 639                 goto out;
 640
 641         ht = iter->ht;
 642
 643         spin_lock(&ht->lock);
 644         if (tbl->rehash < tbl->size)
 645                 list_add(&iter->walker->list, &tbl->walkers);
 646         else
 647                 iter->walker->tbl = NULL;
 648         spin_unlock(&ht->lock);
 649
 650         iter->p = NULL;
 651
 652 out:
 653         rcu_read_unlock();
 654 }
 655 EXPORT_SYMBOL_GPL(rhashtable_walk_stop);
 656
 657 static size_t rounded_hashtable_size(const struct rhashtable_params *params)
 658 {
 659         return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
 660                    (unsigned long)params->min_size);
 661 }
 662
 663 static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
 664 {
 665         return jhash2(key, length, seed);
 666 }
 667
 668 /**
 669  * rhashtable_init - initialize a new hash table
 670  * @ht:         hash table to be initialized
 671  * @params:     configuration parameters
 672  *
 673  * Initializes a new hash table based on the provided configuration
 674  * parameters. A table can be configured either with a variable or
 675  * fixed length key:
 676  *
 677  * Configuration Example 1: Fixed length keys
 678  * struct test_obj {
 679  *      int                     key;
 680  *      void *                  my_member;
 681  *      struct rhash_head       node;
 682  * };
 683  *
 684  * struct rhashtable_params params = {
 685  *      .head_offset = offsetof(struct test_obj, node),
 686  *      .key_offset = offsetof(struct test_obj, key),
 687  *      .key_len = sizeof(int),
 688  *      .hashfn = jhash,
 689  *      .nulls_base = (1U << RHT_BASE_SHIFT),
 690  * };
 691  *
 692  * Configuration Example 2: Variable length keys
 693  * struct test_obj {
 694  *      [...]
 695  *      struct rhash_head       node;
 696  * };
 697  *
 698  * u32 my_hash_fn(const void *data, u32 len, u32 seed)
 699  * {
 700  *      struct test_obj *obj = data;
 701  *
 702  *      return [... hash ...];
 703  * }
 704  *
 705  * struct rhashtable_params params = {
 706  *      .head_offset = offsetof(struct test_obj, node),
 707  *      .hashfn = jhash,
 708  *      .obj_hashfn = my_hash_fn,
 709  * };
 710  */
 711 int rhashtable_init(struct rhashtable *ht,
 712                     const struct rhashtable_params *params)
 713 {
 714         struct bucket_table *tbl;
 715         size_t size;
 716
 717         size = HASH_DEFAULT_SIZE;
 718
 719         if ((!params->key_len && !params->obj_hashfn) ||
 720             (params->obj_hashfn && !params->obj_cmpfn))
 721                 return -EINVAL;
 722
 723         if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
 724                 return -EINVAL;
 725
 726         if (params->nelem_hint)
 727                 size = rounded_hashtable_size(params);
 728
 729         memset(ht, 0, sizeof(*ht));
 730         mutex_init(&ht->mutex);
 731         spin_lock_init(&ht->lock);
 732         memcpy(&ht->p, params, sizeof(*params));
 733
 734         if (params->min_size)
 735                 ht->p.min_size = roundup_pow_of_two(params->min_size);
 736
 737         if (params->max_size)
 738                 ht->p.max_size = rounddown_pow_of_two(params->max_size);
 739
 740         if (params->insecure_max_entries)
 741                 ht->p.insecure_max_entries =
 742                         rounddown_pow_of_two(params->insecure_max_entries);
 743         else
 744                 ht->p.insecure_max_entries = ht->p.max_size * 2;
 745
 746         ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);
 747
 748         /* The maximum (not average) chain length grows with the
 749          * size of the hash table, at a rate of (log N)/(log log N).
 750          * The value of 16 is selected so that even if the hash
 751          * table grew to 2^32 you would not expect the maximum
 752          * chain length to exceed it unless we are under attack
 753          * (or extremely unlucky).
 754          *
 755          * As this limit is only to detect attacks, we don't need
 756          * to set it to a lower value as you'd need the chain
 757          * length to vastly exceed 16 to have any real effect
 758          * on the system.
 759          */
 760         if (!params->insecure_elasticity)
 761                 ht->elasticity = 16;
 762
 763         if (params->locks_mul)
 764                 ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
 765         else
 766                 ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;
 767
 768         ht->key_len = ht->p.key_len;
 769         if (!params->hashfn) {
 770                 ht->p.hashfn = jhash;
 771
 772                 if (!(ht->key_len & (sizeof(u32) - 1))) {
 773                         ht->key_len /= sizeof(u32);
 774                         ht->p.hashfn = rhashtable_jhash2;
 775                 }
 776         }
 777
 778         tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
 779         if (tbl == NULL)
 780                 return -ENOMEM;
 781
 782         atomic_set(&ht->nelems, 0);
 783
 784         RCU_INIT_POINTER(ht->tbl, tbl);
 785
 786         INIT_WORK(&ht->run_work, rht_deferred_worker);
 787
 788         return 0;
 789 }
 790 EXPORT_SYMBOL_GPL(rhashtable_init);
 791
 792 /**
 793  * rhashtable_free_and_destroy - free elements and destroy hash table
 794  * @ht:         the hash table to destroy
 795  * @free_fn:    callback to release resources of element
 796  * @arg:        pointer passed to free_fn
 797  *
 798  * Stops an eventual async resize. If defined, invokes free_fn for each
 799  * element to releasal resources. Please note that RCU protected
 800  * readers may still be accessing the elements. Releasing of resources
 801  * must occur in a compatible manner. Then frees the bucket array.
 802  *
 803  * This function will eventually sleep to wait for an async resize
 804  * to complete. The caller is responsible that no further write operations
 805  * occurs in parallel.
 806  */
 807 void rhashtable_free_and_destroy(struct rhashtable *ht,
 808                                  void (*free_fn)(void *ptr, void *arg),
 809                                  void *arg)
 810 {
 811         const struct bucket_table *tbl;
 812         unsigned int i;
 813
 814         cancel_work_sync(&ht->run_work);
 815
 816         mutex_lock(&ht->mutex);
 817         tbl = rht_dereference(ht->tbl, ht);
 818         if (free_fn) {
 819                 for (i = 0; i < tbl->size; i++) {
 820                         struct rhash_head *pos, *next;
 821
 822                         for (pos = rht_dereference(tbl->buckets[i], ht),
 823                              next = !rht_is_a_nulls(pos) ?
 824                                         rht_dereference(pos->next, ht) : NULL;
 825                              !rht_is_a_nulls(pos);
 826                              pos = next,
 827                              next = !rht_is_a_nulls(pos) ?
 828                                         rht_dereference(pos->next, ht) : NULL)
 829                                 free_fn(rht_obj(ht, pos), arg);
 830                 }
 831         }
 832
 833         bucket_table_free(tbl);
 834         mutex_unlock(&ht->mutex);
 835 }
 836 EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy);
 837
 838 void rhashtable_destroy(struct rhashtable *ht)
 839 {
 840         return rhashtable_free_and_destroy(ht, NULL, NULL);
 841 }
 842 EXPORT_SYMBOL_GPL(rhashtable_destroy);